1. Field of the Invention
The present invention relates to improvement of lubricity of fuels, and more particularly to chemical treatment of low sulfur diesel fuels and spark ignition fuels for improvement of lubricity.
2. Description of the Prior Art
Low sulfur diesel fuels were developed in the early 1990s in response to environmental concerns. Such fuels are prepared by severely hydrotreating diesel components to produce a low sulfur, olefin and aromatic content fuel. Standards have been set for such low sulfur content fuels. According to ASTM Standard Specification for Diesel Fuel Oils D-975-96a low sulfur diesel fuel has a maximum sulfur content of 0.05% based on mass, versus levels as high as 0.5% or more for equivalent standard diesel fuels. As used herein, the phrase xe2x80x9clow sulfur diesel fuelsxe2x80x9d refers to such hydrotreated fuels of maximum sulfur content of 0.05% based on mass.
While such fuels are desirable from an environmental standpoint, they suffer from a serious problem of substantially reduced lubricity. xe2x80x9cLubricityxe2x80x9d refers to the lower friction, wear or scuffing that a liquid may give compared to another liquid of the same viscosity. See, for example, xe2x80x9cThe Lubricity of Diesel Fuels,xe2x80x9d Wei, D. et al., Wear, 111 (1986), pp. 217-235.
Many articles have discussed low sulfur diesel fuels and their poor lubricity characteristics. For example, see xe2x80x9cLubricity Additivesxe2x80x94Performance and No-Harm Effects in Low Sulfur Fuels,xe2x80x9d Batt, R. J., et al., SAE Publication 961943 (1996); xe2x80x9cDevelopment of Laboratory Tests to Predict the Lubricity Properties of Diesel Fuels and the Application to the Development of Highly Refined Diesel Fuels,xe2x80x9d Bovington, C. et al., Tribotest Journal 2xe2x80x942, December 1995, (2) 93 1354-4063; and PCT patent application, International Publication No. WO 94/17160 (Exxon Chemical Patents, Inc.); all of which are incorporated herein by reference. The cited PCT patent publication (p. 1), notes that the poor lubricity of the low sulfur diesel fuel creates a serious problem because xe2x80x9cthe ability of the fuel to lubricate the injection system of the engine is reduced such that, for example, the fuel injection pump of the engine can fail relatively early in the life of an engine . . .xe2x80x9d
This concept of lubricity and lubricity additives, to which the present invention is directed, is distinct from wear-reducing additives as used in lubricants and in lubricity additives. Moreover, although mainly boundary lubrication, where the additive forms a layer between the two metal surfaces, is thought to be operative, mechanisms of providing good lubricity varying from boundary lubrication to hydrodynamic (hydraulic lubrication) have been suggested as the role of lubricity additives.
Thus, U.S. Pat. No. 4,204,481 (Malec) appears to be directed to wear in injectors in conjunction with standard relatively high sulfur content fuel. For instance, in the xe2x80x9cBackground of the Invention,xe2x80x9d Malec reports that certain alcohols have been substituted for conventional petroleum-derived diesel fuels and that while such alcohols (with the addition of certain accelerators) may be used as fuels, they are xe2x80x9cnotably deficient in lubricity or lubricating properties with the result that engine wear from the use of these fuels in internal combustion reciprocating diesel engines is a serious problem . . .xe2x80x9d and of xe2x80x9cparticular concern are wear problems associated with the fuel injector mechanisms used in such engines.xe2x80x9d By contrast, the subject invention is directed to lubricity at fuel pumps, in particular, rotary/distributer pumps, where the lubricant is the fuel itself, and which as a result are the cite of most wear problems as opposed to in-line fuel pumps which are lubricated by engine oil. See, for instance, xe2x80x9cSevere Hydrotreating of Diesel Can Cause Fuel-Injector Pump Failure,xe2x80x9d Booth, M. et al., Oil and Gas Journal, Aug. 16, 1993, pp. 71-76.
As reported in the cited Tribotest Journal article and elsewhere, temperature and wear mechanisms present are critical in determining whether a pump will fail. These considerations of temperature and wear mechanisms emphasize the distinctive nature of the lubricity problem as opposed to the problem of injector wear, to which the cited Malec patent is directed. Injectors, are subjected not only to very high cylinder temperatures (and so operate at much higher temperatures than do fuel pumps), but also to a substantially different wear mechanism than are fuel pumps. In particular, injectors experience linear (up and down) type of wear, while fuel pump wear is the result of sliding and rotary components from the action of the pump. And it has been noted that adhesion, sliding wear, oxidative and fatigue wear are all found in fuel pumps using poor lubricity fuel.
Some lubricity aids have been developed for low sulfur diesel fuels, but each suffers from one or more drawbacks when applied to such fuels. For example, many additives are fatty acids or modified fatty acids and so are acidic in character, which is undesirable due to concerns that they will react or otherwise interfere with the effectiveness of other additives, such as amine surfactants. Other additives are esters, but have several free hydroxide groups on the molecules which cause the additive to exhibit poor water tolerance and high dose rates may be required. Likewise, imidazolines have been found to have poor water tolerance and/or poor hydrolytic stability, resulting in precipitate formation upon extended exposure to moisture. Still other additives increase the tendency of the fuel to form an emulsion and thus to become hazy upon exposure of the fuel to moisture. Generally, however, low sulfur diesel fuels are so new that few lubricity aids have been developed for them, regardless of efficacy or drawbacks.
Moreover, although low sulfur diesel fuel is of particular concern, there is a continual search for new alternative lubricants for spark ignition fuels as well.
The present invention, therefore, is directed to a novel fuel composition of improved lubricity. The fuel composition comprises a lubricity-increasing amount of a lubricity aid dissolved in a fuel selected from the group consisting of low sulfur diesel fuel and spark ignition fuels. The lubricity aid is an alkanolamide of a fatty acid, an alkanolamide of a modified fatty acids or a mixture thereof, provided that if the lubricity aid is other than an alkanolamide of an aryl-substituted fatty acid, the composition further necessarily comprises a haze-reducing amount of a dehazer.
The present invention is also directed to a fuel lubricity additive comprising about 3 to about 20 parts by weight lubricity aid per part by weight dehazer, the lubricity aid being selected from the group consisting of alkanolamides of fatty acids, alkanolamides of modified fatty acids and mixtures thereof.
The present invention is further directed to a method for improving the lubricity of a low sulfur diesel or spark ignition fuel. According to the method, a lubricity-increasing amount of a lubricity aid is added to the fuel. The lubricity aid is selected from the group consisting of alkanolamides of fatty acids, alkanolamides of modified fatty acids and mixtures thereof. If the lubricity aid is an alkanolamide of an aryl-substituted fatty acid, it is preferred that a haze reducing amount of a dehazer is also added to the fuel. If the lubricity aid is other than an alkanolamide of an aryl-substituted fatty acid, a haze-reducing amount of a dehazer must also be added to the fuel.
Among the several advantages of this invention, may be noted the provision of a superior lubricity aid for use in low sulfur diesel fuel and spark ignition fuels; the provision of such aid that does not cause or increase hazing of the fuel when the fuel contacts water; the provision of such aid that is effective when used in relatively low dosage; the provision of such aid that has a low acid number; and the provision of a method for increasing the lubricity of such fuels with such aid.
In accordance with the present invention, it has been discovered that certain alkanolamides of aryl-substituted fatty acids have low acid numbers, yet impart exceptional lubricity to low sulfur diesel fuels and spark ignition fuels and, moreover, if the alkanolamide of an aryl-substituted fatty acidxe2x80x94or even if another low acid number alkanolamide of a fatty acid or modified fatty acidxe2x80x94is used in combination with a dehazer, the tendency of the fuel to haze is notably lessened. Moreover, it has been found that desirable levels of lubricity can be attained with surprisingly low dosages of the lubricity aid.
Thus, the lubricity aid of this invention comprises an alkanolamide of a fatty acid or a modified fatty acid. The alkanolamide may be prepared by reacting an alkanolamine with an acid or modified fatty acid by well known techniques. The term xe2x80x9calkanolaminexe2x80x9d (and so, correspondingly, xe2x80x9calkanolamidexe2x80x9d) is used in its broadest sense to include, for example, monoalkanolamines, dialkanolamines, and so forth. It is believed that almost any alkanolamine can be used, although preferred alkanolamines are lower alkanolamines, generally having from about two to about six carbon atoms. It has been found that it is highly desirable that a hydroxy group or an NH group be located at a position two carbon atoms from the nitrogen that forms the amide. Thus, while use of morpholine resulted in a poor lubricity aid, use of diethanolamine produced excellent lubricity aids. It is also preferred that the alkanolamide have an O or N functionality in addition to the one amino group (that group being a primary or secondary amino group) and the hydroxy group required by the generic name xe2x80x9calkanolamine;xe2x80x9d for example, dialkanolamines and amino-alkanolamines. Thus, suitable alkanolamines include monoethanolamine, diethanolamine, dipropanolamine and, to a lesser extent, aminoethylaminoethanol such as 2-(2-aminoethylamino)ethanol.
It is believed that the fatty acid may be any fatty acid. Thus, for example, any of the common species, such as coco, lauric, stearic, oleic, linoleic, linolenic, ricinoleic, tall oil, tallow acid are suitable. Likewise, modified fatty acids may be used as well. Modified fatty acids are isomeric forms of the natural and common species, such as isostearic acid, and substituted fatty acids in which, for example, an alkyl group (of up to, for example, twelve carbon atoms) or aryl group (of, for example, about six to about eighteen carbon atoms) is substituted for a hydrogen (or at a broken double bond) of the unsubstituted fatty acid. Examples of this latter case with aryl substituents include phenylstearic acid, tolylstearic acid and xylylstearic acid. Although the modified and unmodified fatty acids generally have from about 12 to about 24 carbon atoms, efficacy does not seem to vary within this range.
The alkanolamide may be modified by esterifying the hydroxyl groups remaining after amide formation, for example, with salicylic acid or glycolic acid. However, no improvements have been noted in connection with such esterification, and some esterification reactants, such as acetoacetic acid, have been noted to harm lubricity efficacy.
As noted above, the amide may be formed by well known techniques. For example, in one method, the amine (or amines) and fatty acid (or fatty acids) are mixed together in an amine to carboxylic groups of the acid molar ratio of from about 1.2:1 to about 1:3 and heated to 140xc2x0 C. or higher to drive off water formed in the resulting condensation reaction. In an alternative method, the methyl ester of the acid is formed and then reacted with the amine at a temperature of from about 60xc2x0 C. to about 100xc2x0 C., eliminating methanol. Although the first method is simpler, its yield is lower, generally about 70%, and side reactions of the alkanolamine with itself form undesirable side products which can have a negative impact on the total solubility of the additive in fuel. By contrast, the second method is a more involved manufacturing process and produces extraneous sodium product, but also produces a product of excellent clarity and greater than 90% yield, with no insoluble by-products.
While these techniques for producing the alkanolamide are well known, it is believed that the commercial alkanolamides used as lubricity aids are made by yet a third technique; namely, by reacting the alkanolamide with one or more fatty triglyceride instead of one or more fatty acid, and then separating the glycerin by-product. Here, it has been found that the techniques based on fatty acids rather than fatty triglycerides yield excellent results.
By contrast to the acidic prior art lubricity aids, which can have acid numbers in excess of 120 mgKOH/g of sample, the amides of this invention have been found to have acid numbers of less than about 25 mgKOH/g of sample. Thus, as used herein, xe2x80x9clow acid number lubricity aidsxe2x80x9d refers to active compositions with acid numbers of less than about 25 mgKOH/g of sample. More preferably, the acid number of the lubricity aid is less than about 10 mgKOH/g of sample, and even more preferably less than about 5 mgKOH/g of sample. The most preferred amides have acid numbers of less than about 1 mgKOH/g of sample.
Surprisingly, it has been found that the amide formed from aryl-substituted fatty acid provides excellent lubricity enhancement to the fuels of interest herein. And while certain species and certain fuels may allow their use without a dehazer or further treatment to maintain the water tolerance of the fuel (that is, in some situations the aryl-substituted amide does not unacceptably increasing the tendency of the fuel to form a haze upon contact with water), the use of a dehazer provides superior water tolerance even with the aryl-substituted amides. Thus, it has now been found that the increased tendency to haze associated with lubricity aids is suppressed by inclusion of a dehazer. While the term xe2x80x9cdehazerxe2x80x9d might suggest in certain contexts that the medium to be treated is hazy prior to treatment and that the haziness is reduced or eliminated therefrom, as used herein, it should be understood to refer to prevention or inhibition of haziness as well. Thus, when added to a clear fuelxe2x80x94a fuel that is not hazyxe2x80x94, but that has a tendency to form a haze upon exposure to water, the dehazer will inhibit haze formation upon exposure of the fuel to water. Thus, the dehazer may be described as an emulsion preventative or emulsion inhibitor.
Dehazers are well known in the art as demulsifiers suitable for use in fuels. It is believed that any dehazer for fuel will have some degree of efficacy in the present application. However, particularly effective dehazers have been found to be glycol oxyalkylate polyol blends (such as sold by Petrolite Corporation under the trade designation TOLAD(copyright) 9312), phenol/formaldehyde or alkyl(C1-18)phenol/-formaldehyde resin oxyalkylates modified by oxyalkylation with C1-18 epoxides and diepoxides (such as sold by Petrolite Corporation under the trade designation TOLAD(copyright) 9308), and C1-4 epoxide copolymers cross-linked with diepoxides, diacids, diesters, diols, diacrylates, dimethacrylates or diisocyanates, all of which types are well known in the art, and blends thereof. The glycol oxyalkylate polyol blends may be polyols oxyalkylated with C1-4 epoxides. The alkyl(C1-18)phenol/-formaldehyde resin oxyalkylates modified by oxyalkylation with C1-18 epoxides and diepoxides may be based on, for example, cresol, t-butyl phenol, dodecyl phenol or dinonyl phenol, or a mixture of phenol (such as a mixture of t-butyl phenol and nonyl phenol). By contrast, demulsifiers such as amine oxyalkylates and sulfonates are not useful in fuels and so are not considered dehazers and are not applicable here.
If a dehazer is used, it may be mixed with the lubricity aid to produce a lubricity additive. Generally the additive should comprise about 3 to about 20 parts by weight lubricity aid per part by weight dehazer. The optimal amount and type of dehazer depend on the water emulsifying properties of the fuel to which the lubricity aid is added, as will be readily understood to those of ordinary skill in the art of fuel treatment, particularly demulsification.
The lubricity additive is incorporated by standard techniques into the fuel to be treated. Any poor lubricity fuel (that is, any fuel having undesirably low lubricity) may be treated, including spark ignition fuels such as gasoline and kerosene, although the present lubricity aids are particularly well suited to low sulfur diesel fuel. The amount to be incorporated is simply an amount such that the lubricity aid is present in the fuel in an amount sufficient to increase the lubricity of the fuel. This amount will be referred to herein as xe2x80x9cthe lubricity-increasing amountxe2x80x9d and has been found to be generally from about 10 to about 500 ppm lubricity aid based on weight of the fuel. Preferably, the lubricity aid is used in a concentration of from about 20 to about 100 ppm, more preferably about 10 to about 50 ppm, based on the weight of the fuel.
The dehazer, likewise, should be used in an amount sufficient to inhibit the hazing that might otherwise occur when the fuel without the dehazer contacts water, and this amount will be referred to herein as a xe2x80x9chaze-inhibiting amount.xe2x80x9d Generally, this amount is from about 1 to about 50 ppm based on the weight of the fuel. The relative proportion of lubricity aid toldehazer in the lubricity additive discussed above is coordinated so that appropriate concentrations of both components can be produced in the fuel.
The lubricity aid of this invention has been found to be extremely well-suited to low sulfur diesel fuel, with a very low dosage providing excellent lubricity without producing a hazing problem and without the side-reaction problems associated with acidic lubricity aids. Moreover, it has been found that the lubricity aid of this invention is similarly well-suited for use in spark ignition fuels such as gasoline and kerosine.